I've been thinking for some time now that we should have a sticky thread for safety tips
here in this forum.

Working with electricity can be
dangerous, or even lethal, if you don't follow proper safety precautions. If you are new
to working with electrical circuits and are contemplating embarking on a DIY project along
these lines, there are things you MUST be aware of before you start poking your fingers
into electrical circuits.

Please feel free
to post any safety tips you can offer, or any links to sites that offer safety tips, here
in this thread.

--------------------Scott--Where are we going and why am I in this handbasket?

For starters, I ran across this page recently. The safety tips are mainly aimed at people
wanting to build or work on tube amps, but there are a number of excellent suggestions
there that apply generally to working on electrical circuits.

--------------------Scott--Where are we going and why am I in this handbasket?

Good plan... One thing: in the link you posted, the author says 'be the one-armed
technician'... my college lecturers (when I did a test and repair course) said 'Always
use your right hand - even if you're left handed - keep your left hand in your
pocket!!' That way any large electric shocks go down the right side of your body
rather than the left (near your heart!).

Having said that, I did get something
like a 15kv shock straight across my chest once when I was testing solenoid hydraulic
valves... bare wires in each hand

The one handed approach is good -- especially if working in a rack bay where the natural
tendency is often to hold on to the earthed metal bay with one hand while poking around in
potentially live things with the other

The other thing I would stonrgly recommend is to remove watches and any rings before
working on equipment -- especially valve gear where everything is wired between tag
strips. It is surpsingly easy to foget about the rings or metal watch you might be
wearing, and accidentally short something out, sometimes with very dramatic effects.

It tends not to life threatening to the wearer because being made of metal, these
things conduct the electricity around the wearer rather than through him or her, but it
can make one hell of a mes of the thing you were working on and turn a quick simpole job
into a major rebuild!

I'll second the warning about wedding rings! I don't wear mine any more after seeing the
state of a friend's hand after he shorted a 1000AH 24V battery with one whilst servicing
an OB truck! The ring arced to a terminal, fused to it, melted, and welded itself and his
finger to the battery terminal - in a pretty spectacular and very unpleasant way.

One of the best bits of safety advice I received was from an elderly college professor
who said "always remember that every piece of wire has at least two ends" He went on to
say that just because you can see one end, it doesn't mean that the other isn't connected
to something that can kill you!

This link here not only
provides an excellent on-line course in basic electronics, but also covers electrical
safety and has good introductions on systems and signal which is actually more applicable
to audio but is often lacking in basic electronics textbooks.

My original post got eaten and I don't have time to type another
one so here's the short version.

I like this site for a few reasons:--Very well written with clear explanations, plenty of examples and practical
application.--Written from the standpoint of an electrical technician which is
beneficial for DIY'ers.--A good part (and even a soapbox!) on electrical safety
that's put right after the very basics.--There seems to be a good ammount of
information on troubleshooting (see point 2) when discussing.

Frank has the
right link but here it is again. The URL is short enough to be typed out.

Quote namke:Good plan... One
thing: in the link you posted, the author says 'be the one-armed technician'... my college
lecturers (when I did a test and repair course) said 'Always use your right hand - even
if you're left handed - keep your left hand in your pocket!!' That way any large
electric shocks go down the right side of your body rather than the left (near your
heart!).

Having said that, I did get something like a 15kv shock straight
across my chest once when I was testing solenoid hydraulic valves... bare
wires in each hand

I herd an interesting story from
one of the service engineers at work. I work at a company that makes coal mining machines.
These machines all run on high voltage AC power. Well one day said service engineer was on
a call where a machine went down. Him and the mine electrician were working on the machine
and had the breaker for the machine locked and tagged out. Well the shift ends and the
machine isn't running so the service engineer stays to continue working. Unknown to him
the electrician takes his tag off the breaker. Long story short, the electrician on the
next shift turns the power on and the service engineer gets a 950VAC shock to his right
arm. He's sitting on the ground so the current travels through his arm and out his right
butt cheek. He says it acualy took a chunk out of his rump. Thankfully the engineer lived
to tell the tale and has a nasty scar (so he says, I didn't care to look . Lesson
learned.

Quote Radical Ans: the shift
ends and the machine isn't running so the service engineer stays to continue working.
Unknown to him the electrician takes his tag off the breaker.

I think this goes against Health and Safety
regs, and certainly against good practice. When more than one person is working on a
machine, they should all place their own padlocks or tags on the isolation switch,
specifically so that it can't be turned on until every engineer is happy for that to be
done.

Quote Radical Ans: the shift
ends and the machine isn't running so the service engineer stays to continue working.
Unknown to him the electrician takes his tag off the breaker.

I think this goes against Health and Safety
regs, and certainly against good practice. When more than one person is working on a
machine, they should all place their own padlocks or tags on the isolation switch,
specifically so that it can't be turned on until every engineer is happy for that to be
done.

Lucky the guy is alive...

hugh

From what I've herd safety in a coal mine can
sometimes be lacking. At least in the US. In other countries it's a different story. For
instance, Australian mines are so concerned with safety that they can hardly produce coal
sometimes.

Is that a DC system? Doesn't sound like any AC wiring I've ever encountered. Normal mains
is live (brown) neutral (blue) and earth (green/yellow) and 3-phase used to be live red,
yellow and blue connectors, with a black neutral and yellow/green earth (now, thanks to
european harmonisation it's brown, black and grey lives with a blue neutral).

The closest thing your installation sounds like to me is a 3-phase AC supply and you
have to be bloody careful with those, because when you short yourself across one of the
phases and earth, that's just good old 230VAC, but get yourself between any two of the
three phases and you'll shove over 400VAC across yourself, and you don't want that!

Apart from for powering big 3-phase items (air-handling units on top of buildings
spring to mind), you should only ever have 1 of the three phases in any one room (or in
one whole domestic house, for preference). This is why it's vitally important not to use a
really long extension cord to steal your neighbors electricty, because you could expose
yourself to much higher voltages than usual should there be a fault!

Quote Clunk:I have tried a few
variations on this theme but without much luck, and ideas before I spend £100 on a proper
electrician?

Consulting
a qualified electrician seems the absolute best thing to do - trying to 'experiment' what
works without having proper knowledge of an electrical system is very
hazardous and may even turn out to be lethal. Don't mess with electrics until you know what
you're doing.

Not exactly OT but worth a mention.Threee very dear friends of mine *almost*
shuffled off the mortal coil last week.Playing at an outdoor "do" and the 3 phase
had been wired up wrong. Amps lasted for the first set & then all three blew - one
guys lethally frying the mains tfr down to the chassis ground and sending a swift 400-odd
volts to the earthy side of his guitar jack.Fortunately he wasn`t grabbing anything
& simply got hurled across the stage. And he already had curly hair....

Let`s be CAREFUL out there!RDF`s and mains testers at all times, chaps!

P.S. Can all you techie types refrain from correcting me as to how many volts, where the
earth potential lies, etc. this time? Regardless of my technical coherence or lack
thereof, the message needs to get across.

excellent thread, well worth a sticky. i, too, have long heard the 'one-armed
electrician' rule from a friend who studied electrical engineering at one of the top
research unis in the states. they taught it to freshman in their first circuit class and
the lesson stuck. electricity is one of those topics, along with exotic foods and problem
women, that merit an entire chapter in the 'big book of famous last words' ;-)

Quote Hugh Robjohns:You're
right. The important message is what can happen, not the detail of voltages.

But who on earth managed to mis-wire the mains supplies so utterly incompetently, and
are they still in business, or banged up in prison for attempted manslaughter?

Hugh

Have`nt managed to contact
any of them yet, but apparently it was a smallish private "do" so who knows WHO was
allowed to do the wiring.I agree with you 100% - hopefully the survivors are now
carrying their OWN safety kit, like I have for years!

The only thing I can
think of here is that somehow they wound up being on 2 different phases at the same time,
but surely an RDF would have seen this immediately and killed the power? The idea that
anyone would hook up a temporary 3 phase supply without automatically fitting some sort of
safety devices (particularly with the weeather we have been having recently) makes me
shudder.

Might have been a faulty neutral. Get this happen quite a lot on 3 phase machinery. As
long as the phases remain in balance nobody notices, but as soon as someone puts a
significant load from one phase to the (faulty) neutral all bets are off.

--------------------If I had a pound for every time I was told to grow up...
I could have the worlds greatest train set!

Quote damoore: None of them say
"you are across two phases of a three phase".

Remember that standard practice is totally different in your part
of the world and (as I understand it) things like tumble driers are commonly wired across
two phases of a three phase supply in the US.

If you don't have a good
knowledge of the standard wiring practices of the country that you are in then leave all
mains wiring to someone who does. There are massive differences between the US and UK.

There doesn't appear to have been much
further news after the incident, perhaps because of the possible big bucks involved and
concerns about liability. From what was reported it sounded like the insulation had
broken on a disused underground mains cable that hadn't been isolated, and current to
earth created a large enough potential difference at ground level to kill the two horses.
All the stuff in the reports about the other horses being saved because they were wearing
aluminium shoes couldn't have been right though - the danger zone was probably very
localised and they missed it, or got away sufficiently quickly.

Evidently the
fault current was insufficient to blow a fuse or trip a circuit breaker, which is strange
considering that the cable should have been armoured and the metal armour strands
connected to earth at both ends and, probably, to neutral at the supply end. But then
again, the cable shouldn't have been live in the first place so it might not have been
intentionally connected via a protection device.

To do this solder a conventional sewing needle to a test
lead in place of the normal probe (it is surprisingly easy to solder to the eye of a new
needle). Try and make this joint as small and smooth as possible.

Then use
the insulation from a thin wire to make a sleeve that goes over the needle itself right up
to the joint and only leaving 2-3mm of the point exposed. Hold this in place with
heatshrink tubing going over the joint and about 10mm either side. Put another piece of
heatshrink on top of this going about 15mm either side, so you have a small firm 'probe'
that's reasonably well insulated - not suitable for high voltage work!

Your
new probes are ideal for testing chips and surface mount stuff as they are small enough
for you to actually see what you're hitting and far less likely to accidentally bridge
across two legs. Also, the very sharp points will easily punch through dirt and oxides,
and even most PCB varnishes.

With care, you can also use them to spike
through the insulation of ribbon cables etc. when you have possible faulty connectors.

P.S.
After you've stabbed yourself with them a few times, you'll learn to
respect them

--------------------If I had a pound for every time I was told to grow up...
I could have the worlds greatest train set!

Quote Folderol:More for
protecting what you're working on than for yourself...

Make a pair of needle
probes.

To do this solder a conventional sewing needle to a test lead in place
of the normal probe (it is surprisingly easy to solder to the eye of a new needle). Try
and make this joint as small and smooth as possible.

Then use the insulation
from a thin wire to make a sleeve that goes over the needle itself right up to the joint
and only leaving 2-3mm of the point exposed. Hold this in place with heatshrink tubing
going over the joint and about 10mm either side. Put another piece of heatshrink on top of
this going about 15mm either side, so you have a small firm 'probe' that's reasonably well
insulated - not suitable for high voltage work!

Your new probes are ideal for
testing chips and surface mount stuff as they are small enough for you to actually see
what you're hitting and far less likely to accidentally bridge across two legs. Also, the
very sharp points will easily punch through dirt and oxides, and even most PCB
varnishes.

With care, you can also use them to spike through the insulation of
ribbon cables etc. when you have possible faulty connectors.

P.S.After
you've stabbed yourself with them a few times, you'll learn to respect them

Not at all Dave, I've attached a piccy of the probes I made quite a few years ago. I used
the leads from a pair crappy probes - just cut them off. Must have taken me all of 15
minutes.

The points have never needed sharpening, and will poke through just
about anything, unlike ordinary brass ones. They also don't have the ridiculously long
exposed metal that standard probes have.

I have to watch the other engineers
as they are inclined to attempt to 'borrow' them, and our apprentice is very pleased with
himself have recently made a pair of his own, only he stuck to the 2mm exposed length
(having recently experienced the death of a chip).